1. Field of the Invention
The invention relates to an optical imaging device, in particular an objective for microlithography in the field of EUVL for producing semiconductor elements, having a beam path, a plurality of optical elements and a diaphragm device with an adjustable diaphragm opening shape.
2. Description of the Related Art
It is generally known to use various diaphragms as system diaphragms in optical imaging devices. The diameter of the light beam bundle in the beam path of the optical imaging device can be varied by means of these diaphragms, of which the opening diameter can be varied, in particular.
So-called iris diaphragms, which have at least four—but mostly more—thin blades which are generally in the shape of a sickle and are supported at one end rotatably in a fixed mount are particularly widespread. In this arrangement, the other end is provided as guiding device with a pin which is inserted in a groove or slot of a rotatable ring such that the rotation of the rotatable ring moves the blades in such a way that the remaining opening diameter for the diaphragm can be varied.
DE 101 11 299 A1 discloses such an iris diaphragm, in particular for an exposure objective in semiconductor lithography, having a plurality of blades which are guided with the aid of guide elements, and can be moved by at least one drive device for the purpose of adjusting the diaphragm opening. The guide elements are designed such that the blades can be moved in an at least approximately linear fashion in a radial direction in relation to the optical axis of the iris diaphragm.
DE 199 55 984 A1 discloses a further diaphragm for stopping down an optical imaging device.
Known diaphragms, in particular the iris diaphragms which can be adjusted continuously via blades, are less suitable for use in stopping down an optical system used in microlithography, chiefly in the field of EUVL, since more stringent demands are placed here on the installation space available, which these cannot satisfy because of their construction.